This invention relates generally to moisture barrier bags of the type used to transport and store semiconductor wafers, and more particularly to a bag having a window for optically inspecting wafers contained in the bag.
Semiconductor wafers such as those used in various electronics applications may be damaged if contacted by moisture because water chemically attacks semiconductor materials. To inhibit moisture contact, semiconductor wafers are usually stored and transported in some type of moisture barrier. Typically, the moisture barriers are flexible bags which are sealed around transparent boxes containing transparent cassettes which hold several wafers vertically on edge. Thus, the cassettes prevent the wafers from contacting each other, the boxes prevent contact with external objects, and the bags prevent contact with moisture. In the past, the moisture barrier bags were made entirely of low cost materials having ultra-low moisture transmission rates. One such material is an opaque laminate made by vapor depositing aluminum on clear acrylar polymer sheet. Because the laminate is opaque, technicians and machines are unable to optically inspect the contents of the bags. Therefore, the type and number of wafers contained in an opaque bag cannot be confirmed without opening it. However, opening the bag may introduce moisture into the bag thereby defeating its purpose. Moreover, bags made entirely of transparent materials have proved unsatisfactory because they typically have higher moisture transmission rates and cost more than bags made of opaque materials.